I use the following code to set the affinity for processor groups and CPUs:
[StructLayout(LayoutKind.Sequential, Pack = 4)]
private struct _GROUP_AFFINITY
{
public UIntPtr Mask;
[MarshalAs(UnmanagedType.U2)]
public ushort Group;
[MarshalAs(UnmanagedType.ByValArray, SizeConst = 3, ArraySubType = UnmanagedType.U2)]
public ushort[] Reserved;
}
[DllImport("kernel32", SetLastError = true)]
private static extern Boolean SetThreadGroupAffinity(
IntPtr hThread,
ref _GROUP_AFFINITY GroupAffinity,
ref _GROUP_AFFINITY PreviousGroupAffinity);
[DllImport("kernel32", SetLastError = true)]
private static extern IntPtr GetCurrentThread();
/// <summary>
/// Sets the processor group and the processor cpu affinity of the current thread.
/// </summary>
/// <param name="group">A processor group number.</param>
/// <param name="cpus">A list of CPU numbers. The values should be
/// between 0 and <see cref="Environment.ProcessorCount"/>.</param>
public static void SetThreadProcessorAffinity(ushort groupId, params int[] cpus)
{
if (cpus == null) throw new ArgumentNullException(nameof(cpus));
if (cpus.Length == 0) throw new ArgumentException("You must specify at least one CPU.", nameof(cpus));
// Supports up to 64 processors
long cpuMask = 0;
foreach (var cpu in cpus)
{
if (cpu < 0 || cpu >= Environment.ProcessorCount)
throw new ArgumentException("Invalid CPU number.");
cpuMask |= 1L << cpu;
}
var hThread = GetCurrentThread();
var previousAffinity = new _GROUP_AFFINITY {Reserved = new ushort[3]};
var newAffinity = new _GROUP_AFFINITY
{
Group = groupId,
Mask = new UIntPtr((ulong) cpuMask),
Reserved = new ushort[3]
};
SetThreadGroupAffinity(hThread, ref newAffinity, ref previousAffinity);
}